1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, to a semiconductor device having a capacitor and a method of manufacturing the same.
2. Description of the Related Art
As the nonvolatile memory that can stores the information after the power supply is turned OFF, the flash memory and the ferroelectric memory (FeRAM) are known.
The flash memory has the floating gate buried in the gate insulating film of the insulated gate field effect transistor (IGFET), and stores the information by accumulating the charge, as the stored information, in the floating gate. In order to write and erase the information, tunnel current must be supplied to the gate insulating film, which requires a relatively high voltage.
The FeRAM has the ferroelectric capacitor that stores the information by utilizing the hysteresis characteristic of the ferroelectric substance. The ferroelectric film formed between the upper electrode and the lower electrode in the ferroelectric capacitor causes the polarization in response to the value of the voltage applied between the upper and lower electrodes, thereby leaving the spontaneous polarization after the applied voltage is removed. When the polarity of the applied voltage is reversed, the polarity of the spontaneous polarization is also reversed. The information can be read by detecting the polarity and the magnitude of this spontaneous polarization.
The FeRAM has an advantage in that it operates with lower voltage and higher writing speed at lower power consumption than the flash memory.
As set forth in Patent Application Publication (KOKAI) 2001-60669, for example, the memory cell of the FeRAM has the MOS transistor formed on the silicon substrate, the first interlayer insulating film formed on the silicon substrate and the MOS transistor, the ferroelectric capacitor formed on the first interlayer insulating film, the second interlayer insulating film formed on the ferroelectric capacitor and the first interlayer insulating film, the conductive plug buried in the hole that is formed in the first and second interlayer insulating films and connected to the MOS transistor, the first wiring pattern for connecting the conductive plug and the upper electrode of the ferroelectric capacitor, the third interlayer insulating film formed on the first wiring pattern and the second interlayer insulating film, and the second wiring pattern formed on the third interlayer insulating film.
The interlayer insulating film for covering the ferroelectric capacitor has a strong compressive stress, which generates a force in the direction that the insulating film itself expands. As a result, a shrinkage force is applied to the ferroelectric capacitor every time when the interlayer insulating films are formed on the ferroelectric capacitor to overlap with each other, which causes the degradation of the characteristics of the ferroelectric capacitor.
Also, when the first wiring pattern is formed of aluminum, the residual polarization characteristic of the ferroelectric capacitor degrades due to a tensile force of the first wiring pattern. In contrast, in Patent Application Publication (KOKAI) 2001-36025, it is set forth that the aluminum film is heated at the temperature exceeding a Curie point of the ferroelectric film of the ferroelectric capacitor for the purpose of relaxing the tensile force and, after that, the wiring pattern is formed by patterning the aluminum film.
However, since there exists the interlayer insulating film in the gaps between the first wiring pattern, there remains problem that the compressive stress of the interlayer insulating film degrades the ferroelectric capacitor, irrespective of the stress of the first wring pattern.
In contrast, in Patent Application Publication (KOKAI) Hei 11-330390, it is set forth that the interlayer insulating film is formed to have the tensile stress to the ferroelectric capacitor. However, the interlayer insulating film having the tensile stress contains a large amount of moisture, which poses another problem that moisture degrades the capacitor.